update rfc: database schema design

rfcs/0001-core-reservation.md

@@ -29,6 +29,13 @@ enum ReservationStatus {
     BLOCKED = 3;
 }
 
+enum ReservationUpdateType {
+    UNKNOWN = 0;
+    CREATE = 1;
+    UPDATE = 2;
+    DELETE = 3;
+}
+
 message Reservation {
     string id = 1;
     string user_id = 2;
@@ -92,16 +99,88 @@ message QueryRequest {
     google.protobuf.Timestamp end = 5;
 }
 
+message ListenRequest {}
+message ListenResponse {
+    int8 op = 1;
+    Reservation reservation = 2;
+}
+
 service ReservationService {
     rpc reserve(ReserveRequest) returns (ReserveResponse);
     rpc confirm(ConfirmRequest) returns (ConfirmResponse);
     rpc update(UpdateRequest) returns (UpdateResponse);
     rpc cancel(CancelRequest) returns (CancelResponse);
     rpc get(GetRequest) returns (GetResponse);
     rpc query(QueryRequest) returns (stream Reservation);
+    // another system could monitor newly added/confirmed/cancelled reservations
+    rpc listen(ListenRequest) returns (stream Reservation);
 }
 ```
 
+### Database schema
+
+We use postgres as the database. Below is the schema:
+
+```sql
+CREATE SCHEMA rsvp;
+CREATE TYPE rsvp.reservation_status AS ENUM ('unknown', 'pending', 'confirmed', 'blocked');
+CREATE TYPE rsvp.reservation_update_type AS ENUM ('unknown', 'create', 'update', 'delete');
+
+CREATE TABLE rsvp.reservations (
+    id uuid NOT NULL DEFAULT uuid_generate_v4(),
+    user_id VARCHAR(64) NOT NULL,
+    status rsvp.reservation_status NOT NULL DEFAULT 'pending',
+
+    resource_id VARCHAR(64) NOT NULL,
+    timespan TSTZRANGE NOT NULL,
+
+    note TEXT,
+
+    CONSTRAINT reservations_pkey PRIMARY KEY (id),
+    CONSTRAINT reservations_conflict EXCLUDE USING gist (resource_id WITH =, timespan WITH &&)
+);
+CREATE INDEX reservations_resource_id_idx ON rsvp.reservations (resource_id);
+CREATE INDEX reservations_user_id_idx ON rsvp.reservations (user_id);
+
+-- if user_id is null, find all reservations within during for the resource
+-- if resource_id is null, find all reservations within during for the user
+-- if both are null, find all reservations within during
+-- if both set, find all reservations within during for the resource and user
+CREATE OR REPLACE FUNCTION rsvp.query(uid text, rid text, during: TSTZRANGE) RETURNS TABLE rsvp.reservations AS $$ $$ LANGUAGE plpgsql;
+
+-- resevation change queue
+CREATE TABLE rsvp.reservation_changes (
+    id SERIAL NOT NULL,
+    reservation_id uuid NOT NULL,
+    op rsvp.reservation_update_type NOT NULL,
+);
+
+-- trigger for add/update/delete a reservation
+CREATE OR REPLACE FUNCTION rsvp.reservations_trigger() RETURNS TRIGGER AS $$
+BEGIN
+    IF TG_OP = 'INSERT' THEN
+        -- update reservation_changes
+        INSERT INTO rsvp.reservation_changes (reservation_id, op) VALUES (NEW.id, 'create');
+    ELSIF TG_OP = 'UPDATE' THEN
+        -- if status changed, update reservation_changes
+        IF OLD.status <> NEW.status THEN
+            INSERT INTO rsvp.reservation_changes (reservation_id, op) VALUES (NEW.id, 'update');
+        END IF;
+    ELSIF TG_OP = 'DELETE' THEN
+        -- update reservation_changes
+        INSERT INTO rsvp.reservation_changes (reservation_id, op) VALUES (OLD.id, 'delete');
+    END IF;
+    -- notify a channel called reservation_update
+    NOTIFY reservation_update;
+    RETURN NULL;
+END;
+END
+$$ LANGUAGE plpgsql;
+CREATE TRIGGER reservations_trigger
+    AFTER INSERT OR UPDATE OR DELETE ON rsvp.reservations
+    FOR EACH ROW EXECUTE PROCEDURE rsvp.reservations_trigger();
+```
+
 Explain the proposal as if it was already included in the language and you were teaching it to another Rust programmer. That generally means:
 
 - Introducing new named concepts.